Intrinsic cardiac neurons as the consulate general of the brain in the heart: A review

Abstract

Contrary to the prevailing understanding about one-way communication from brain to heart, recent research has unveiled a two-way communication pathway between these two organs, featuring the delivery of signals from the cardiac afferents to the brain. While the medulla oblongata is known to send autonomic signals for cardiac function regulation, 80% of the vagal afferents send signals to the brain for cardiac regulation. The vagus nerve receives these signals from the intrinsic cardiac neurons, often referred to as “the little brain of the heart.” Intrinsic cardiac neurons are neuronal structures with the same biochemical profile as neurons, communicating with the vagus nerve through acetylcholine and expresses markers of neuronal function such as tyrosine hydroxylase and others. Intrinsic cardiac neurons also influence the autonomic system, which can be studied through heart-rate variability measures. Heart rate variability (HRV) is altered in many types of cardiac disorders and is a well-known measure for studying short- and long-term disease-related variations in cardiac function. Some psychiatric disorders such as post-traumatic stress disorder, schizophrenia, and major depression also exhibited alterations in HRV. HRV is related to heartbeat-evoked potentials (HEPs) and electrical potentials in the brain that are influenced by the heart. HEPs are altered in disease states and can be impacted by environmental factors. This paper reviews the existing literature concerning intrinsic cardiac neurons and their possible role in heart-brain communication.